Part 14

The Yule Marble, or Yule Colorado Marble, was produced by metamorphism of Leadville Limestone in an area intruded by the Treasure Mountain Granite, thirty-five miles south of Glenwood Springs. This exquisite marble, which has graced many famous monuments and buildings (among them the Lincoln Memorial and the Tomb of the Unknown Soldier), is known for its almost uniform snowy whiteness and regular, fine crystallization. Although its beauty, massive character, and uniformity made it a sought-after ornamental stone, quarrying was economically marginal because of the remoteness of the site. In spite of this, nearly $7,000,000 worth of the marble was produced before the quarry closed in 1940.

The Lyons area, north of Boulder, provides pink, hard, even-grained sandstone which splits readily into slabs or flagstones. These are used in the Denver-Boulder area for sidewalks and patios as well as for facing buildings. Quarries owned by the University of Colorado provide a constant supply of handsome facing material and flagstone for new university buildings, although in recent years the high cost of stone construction has limited its use on the campus.

The Lyons Sandstone was deposited as beach and bar sand along the edge of a sea which lay east of the Front Range in Permian time. After deposition, the sand was deeply buried and compacted. Now tilted up along the Front Range uplift, it comes to the surface along the east side of the range. Only between Fort Collins and Boulder does the stone have the desirable combination of hardness, thin-beddedness, and color which makes it desirable for ornamental use. The pink color of the Lyons Sandstone is derived from iron oxides, mostly hematite, disseminated between the sand grains. Dendrites (often erroneously called fossil ferns or plants) ornament some slabs; they were formed by crystallization of manganese dioxide from groundwater as it slowly percolated through the rock.

Lime and Gypsum

Outcrops of the Cretaceous Greenhorn and Niobrara Limestones provide most of the cement materials in Colorado. A number of plants along the mountain front, including a completely automated and dust-free one near Lyons, provide the major population centers with millions of tons of cement each year.

Colorado is richly endowed with gypsum, useful in cement and plaster manufacture and for ornamental stone and sculpture. Along the eastern front of the mountains, gypsum occurs in the Triassic Lykins Formation; in the Mountain Province, it is abundant in Pennsylvanian sedimentary rocks. Particularly high-quality Pennsylvanian gypsum is quarried at the town of Gypsum, west of Eagle.

The Colorado portion of the Paradox Basin, in the Plateau Province, contains immense deposits of Pennsylvanian gypsum. Here, rocks near the surface have been pushed up into sharp northwest-trending faulted anticlines by upward movements of gypsum and salt from depths of several thousands of feet. The soluble salt and gypsum cores of these structures have been washed away more rapidly than the surrounding layers of sandstone and shale, leaving depressions such as Gypsum Valley, Paradox Valley, and Sinbad Valley, on the crests of the anticlines. Red and yellow Triassic sandstones and shales, especially the Chinle Formation and the Wingate Sandstone, dip away from these valleys. Exploratory wells indicate that vast masses of salt and gypsum are present beneath the surface, and may extend to depths greater than 10,000 feet.

GEMS AND ORNAMENTAL STONES

More than thirty different gems and ornamental stones are known to occur in Colorado. Amazonstone, amethyst, garnet, tourmaline, aquamarine, topaz, lapis lazuli, quartz crystal, smoky and rose quartz, sapphire, several varieties of agate, zircon, and other attractive stones are gathered within the state, mainly in the Mountain Province. Turquoise is known at several places in the volcanic area of southern Colorado. Alabaster is mined along the northeastern mountain front near Fort Collins and Loveland. Localities of interest to gem hunters are described in Colorado Gem Trails and Mineral Guide, by Richard M. Pearl.

Gem Village, in southwestern Colorado on U. S. highway 160 between Durango and Pagosa Springs, is a favorite stopping place for tourists wishing to see or buy colorful and attractive Colorado stones such as petrified wood, agatized dinosaur bones, chalcedony, and jasper.

WATER

Although not all aspects of water and water supply are geologic, water is an important geologic agent, determining the shape of the surface, the distribution of minerals, and the location of caves. Water used in Colorado comes entirely from precipitation within the state, as all of Colorado’s rivers flow from Colorado outward toward the surrounding lower-elevation states.

Surface Water

Moisture carried by prevailing westerly or northwesterly winds falls primarily on Colorado’s western slope, although at some times of year precipitation may come from the northeast or southeast. West of the continental divide, where population is sparse, there is a surplus of water. East of the divide, where more than 90 per cent of the population lives, water is in desperately short supply. The high and largely unpopulated Mountain Province receives by far the greatest proportion of precipitation, while agricultural areas of the Prairie and Plateau Provinces receive much less. Needless to say, the major problem involving water in Colorado is how to move it from areas where it is abundant to areas where it is needed.

In many parts of the state, complex water laws and complicated irrigation canals and water systems were developed soon after the area became settled. Gradually but inevitably, water resources have been transferred from the western slope to the eastern. However, such transfer must be undertaken with due regard for the rights of downstream users, notably California, Arizona, and New Mexico.

One of the largest water movement schemes in the state is the Colorado-Big Thompson Project. Water that otherwise would flow into the Colorado River is piped from Grand Lake through the Alva B. Adams tunnel under the high mountains of Rocky Mountain National Park, and into the Big Thompson drainage near Estes Park. It then travels through a series of reservoirs and tunnels into the South Platte River basin, where it is used for irrigation and household water. The water is pumped up the western gradient of this system by electric power produced as it flows down the eastern slope. Surplus electric power serves the Colorado-Wyoming area.

Another large project is the Denver Water Board’s Dillon Reservoir Project, in which western slope water collected at Dillon is pumped twenty-three miles under the continental divide through the Harold D. Roberts tunnel to the North Fork of the South Platte River for use by the city of Denver. The exit point of this tunnel can be seen a few miles west of Grant along U. S. highway 285. This project is continuously growing as Denver’s water needs mount.

In each of these projects, engineering geologists played a prominent part in locating dams and tunnels that would not leak or fail, and that could collect and transport a maximum amount of water during the high-runoff spring season for distribution through the rest of the year. Fortunately for geologists, the tunnels and bores necessary to the projects allowed them to learn a great deal about the structure of the interior of the high mountains, and helped to improve their interpretation of earth history in this most interesting region.

The necessity for storing irrigation water along the eastern mountain front has led to the creation of hundreds of new lakes in the region. Although water levels vary with the season, many of the lakes provide opportunities for water sports and recreation for the burgeoning inland population.

Two large dams have recently been built in western Colorado for another purpose: to control the flow of water in the Colorado River drainage basin. Electric power for western Colorado also comes from these dams. One of the dams is on the Gunnison River at Curecanti, upstream from the Black Canyon of the Gunnison National Monument, and the other is on the Frying Pan River near Ruedi. The latter was completed over the objections of geologists, who believed that the extensive gypsum deposits underlying the damsite would cause its failure. Cement pumped deep into the rocks in the vicinity has so far prevented serious rupture.

There is strong resistance by conservation groups to the construction of more dams on Colorado River drainage, primarily because the Colorado and its tributaries pass through many irreplaceable canyons, some of them parts of National Parks and Monuments, that are very much a part of our western heritage.

Groundwater

SAN JUAN MOUNTAINS LIMIT OF FLOWING WELLS HUBBARD’S WELL OTTOWAY’S WELL ALAMOSA WELL GEORGE NEWSOM’S WELL CALKIN’S WELL LIMIT OF FLOWING WELLS Moraine Alluvial Slope SANGRE DE CRISTO MOUNTAINS Sands, lava beds, gravels, conglomerates, etc. Alamosa formation Granites WEST SANTE FE FORMATION SANTE FE FORMATION EAST

Groundwater is extremely important to Colorado, especially in the Prairie Province and the San Luis Valley. Below these two areas lie a number of distinct and productive groundwater aquifers, several of them artesian. In Otero County, for example, there are five major aquifers: three separate Quaternary gravel deposits, the Cretaceous Dakota Sandstone, and the Cheyenne Sandstone Member of the Purgatoire Formation, also Cretaceous. All these aquifers are characterized by their high porosity and permeability, which allow water to flow rapidly through them. Wells in the younger, shallower aquifers produce as much as 2,000 gallons per minute; those in the older, deeper aquifers produce about eighty gallons per minute, some of it with an artesian “head.”

The San Luis Valley supports intensive agriculture, made possible by a great artesian water supply. A thick series of soft interlayered clays and sands, the Alamosa Formation, slopes down toward the center of the basin from the surrounding mountains. Water entering the sandstone beds at the mountain edges flows through the sand layers held there by the impermeable clay beds. By the time it reaches the center of the valley, it has developed considerable hydrostatic head, and the water rises in wells without pumping. Unfortunately, both the irrigation water and the soils in the San Luis Valley are highly alkaline. Constant evaporation from the irrigated fields has concentrated the alkali near and on the surface, rendering some of the land less usable than it was originally.

Caves

Colorado has many caves, most of them carved by underground water in Paleozoic limestone. The Cave of the Winds at Manitou is the only one in the state which has been developed as a tourist attraction. It is in highly faulted Ordovician and Mississippian limestone near the mountain front, where the faulting, coupled with the high relief, has accelerated solution of the rock by allowing groundwater to percolate downward rapidly. The cavern was probably carved during the Pleistocene Ice Age, when surface water and groundwater were much more abundant than at present. Deposition of stalactites and stalagmites has occurred within the last few thousand years, as supplies and movement of water have decreased.

Spanish Cave, above timberline on Marble Mountain in the Sangre de Cristo Range, is probably the nation’s highest limestone cave. It is in thick folded and faulted Pennsylvanian reef limestone, at an elevation of over 12,000 feet. The cave has many intricate passageways branching from its main vertical tubes and channels.